Ecology of Borrelia burgdorferi in ticks (Acari : Ixodidae), rodents, and birds in the Sierra Nevada foothills, placer county, California

This study examined the prevalence of Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner in host-seeking adult and nymphal Ixodes pacif icus Cooley & Kohls and estimated the I. pacificus infestation and B. burgd orferi infection of rodent and avian hosts in the western Sierra Nevada foo thills of northern California. Additionally, we identified species likely t o participate in an enzootic cycle for B. burgdorferi in this yellow pine t ransition habitat. Evidence of infection with B. burgdorferi was identified in 7.3 and 5.4% of host-seeking I. pacificus adults and nymphs, respective ly. Mean numbers of I. pacificus observed on rodents were 1.15 for Neotoma fuscipes Baird and 0.18 for Peromyscus spp. One of 104 ear punch tissues ob tained from woodrats and none from 49 Peromyscus spp. yielded B. burgdorfer i. A total of 291 collected birds representing 34 species had a mean of 0.2 7 I. pacificus per bird. The mean I. pacificus infestation of ground-dwelli ng birds was 2.5 ticks per bird. Forty-nine of 92 (53%) blood smears collec ted from birds were reactive to a B. burgdorferi specific antibody. This st udy presents the identification of a B. burgdorferi-like spirochete in bird s in western North America. The tick burden and spirochete infection of bir ds suggests that birds may be involved in a local B. burgdorferi enzootic c ycle and likely participate in the transport of ticks and spirochetes to ot her locations while rodents from this site do not appear to be major contri butors.